public class MyLinkedList implements IList{

    static class ListNode{
        int val;
        ListNode next;
        ListNode prev;
        ListNode(int val){
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode last;

    @Override
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if(head == null){
            head=node;
            last=node;
        }
        else{
            head.prev=node;
            node.next=head;
            head=node;
        }
    }

    @Override
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if(head == null){
            head=node;
            last=node;
        }
        else{
            last.next=node;
            node.prev=last;
            last=node;
        }
    }

    @Override
    public void addIndex(int index, int data) {
        if(index < 0 || index > size()){
            throw new PosIllegality("获取下标异常！！！");
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if(index == size()){
            addLast(data);
            return;
        }
        ListNode cur=findIndex(index);
        ListNode node=new ListNode(data);
        cur.prev.next=node;
        node.next=cur;
        node.prev=cur.prev;
        cur.prev=node;
    }

    private ListNode findIndex(int index) {
        ListNode cur = head;
        while (index != 0) {
            cur = cur.next;
            index--;
        }
        return cur;
    }

    @Override
    public boolean contains(int key) {
        if(head == null){
            return false;
        }
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    @Override
    public void remove(int key) {
        ListNode cur=head;
        while (cur != null) {
            if(cur.val == key){
                cur.next.prev=cur.prev;
                cur.prev.next=cur.next;
                return;
            }
            cur=cur.next;
        }
    }

    @Override
    public void removeAllKey(int key) {
        ListNode cur=head;
        while (cur != null) {
            if(cur.val == key){
                cur.next.prev=cur.prev;
                cur.prev.next=cur.next;
            }
            cur=cur.next;
        }
    }

    @Override
    public int size() {
        ListNode cur = head;
        int count = 0;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }

    @Override
    public void clear() {
        ListNode cur=head;
        while (cur != null) {
            ListNode curNext=cur.next;
            cur.prev=null;
            cur.next=null;
            cur=curNext;
        }
        head=null;
    }

    @Override
    public void display() {
        ListNode cur=head;
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }
}
